Coating composition for tendon for prestressed concrete

ABSTRACT

Disclosed is a coating composition for PC tendon, which is applied on surface of the PC tendon. This composition includes epoxy resin, multifunctional isocyanate compound, calcium oxide and water, and further includes water-absorbing polymer as necessary. A curing time thereof is adjusted so that tensioning by the PC tendon can be exerted 30 days or later after casting of the concrete. Accordingly, even when applied to a massive concrete structure, the coating composition enables effective tensioning after hardening of the concrete, while exhibiting excellent storage stability.

TECHNICAL FIELD

The present invention relates to a coating composition applied on asurface of PC (Prestressed Concrete) steel product or the like used astendon in post-tensioning system of prestressed concrete for the purposeof preventing rust and corrosion as well as integrating the tendon withthe concrete.

BACKGROUND ART

Concrete used in various constructions has a disadvantage ofvulnerability to tension force. In order to compensate for thisdisadvantage, there has been known concrete provided with improvedtension strength by preliminarily applied compression force with PCtendon. This concrete is called as prestressed concrete. As arepresentative method of producing such prestressed concrete,post-tensioning system has been known.

A general production method of prestressed concrete by thispost-tensioning system is described below. Before casting of concrete,sheath member is disposed in the concrete. Then, PC tendon (PC steelwire, PC steel twist wire, PC hard steel wire, PC steel rod, continuousfiber, or the like) is inserted into the sheath member. After hardeningof the concrete, the PC tendon is tensioned by means of a tensioningmachine. After that, in order to prevent the PC tendon from rusting andbecoming eroded as well as to achieve adhesion and integration of the PCtendon with the concrete, cement milk or the like is injected betweenthe sheath member and the PC tendon.

However, according to this method, the operations of inserting the PCtendon into the sheath member and injecting the cement milk or the likeare very complicated. As the result, this method requires great time andlabor, leading a drawback of cost rise. In addition, since the spacebetween the inserted PC tendon and the sheath member is very narrow, andthe PC tendon is arranged in a curved manner, it is difficult tocompletely fill the whole of the sheath member with the cement milk orthe like, so that the tendon may be corroded in the defectively filledregion.

In order to solve the above problems, there have been proposed methodsof preliminarily coating the surfaces of tendon with coating material(see, for example, Japanese Examined Patent Publication No. HEI 3-28551(1991), Japanese Examined Patent Publication No. SHO 53-47609 (1978) andthe like). These methods can be generally classified into (1) thosegiving anti-rust and anti-corrosion effects and (2) those improvingadhesion between concrete and the tendon while giving anti-rust andanti-corrosion effects.

In a typical example of methods (1), epoxy resin as coating material iselectrostatic-coated on the surface of PC steel material as tendon.Although anti-rust and anti-corrosion effects can be exerted by thismethod, the coating material is brought into a completely cured state onthe surface of the tendon. Therefore, when this method is used in apost-tensioning system, insertion of the tendon into sheath member andgrouting operation for integrating the concrete and the tendon are stillrequired as is the case of usual post-tensioning system, so that theproblem of cost rise remains unsolved.

On the other hand, one exemplary method of the above classification (2)uses so-called unbonding PC steel material obtained by applying greaseas coating material on the surface of PC steel material as tendon andcovering the resultant PC steel material with sheath member such aspolyethylene or the like. In this method, before casting of concrete,the above-mentioned unbonding PC steel material is arranged. Afterhardening of the concrete, the PC steel material is tensioned. When thePC steel material is tensioned, the tension strength is transmittedalong the whole length of the PC steel material because the fluid greaseexists between the concrete and the PC steel material. Accordingly,metal sheath member used in usual post-tensioning system is no longernecessary, with the result that insertion of the tendon into the sheathmember as well as grouting operation for injecting cement milk or thelike are no longer required. Therefore, the problem of cost rise whichis one disadvantage of usual post-tensioning systems can be solved.

However, the above method has disadvantages of poor bending strength andpoor fatigue strength of concrete since the grease as coating materialwill never be cured, and the tendon will never bond to the concrete.

As a technique for solving the above disadvantage accompanying themethod using the above-mentioned unbonding steel material, also proposedis a method that thermo-curing composition in uncured state as coatingmaterial is applied on the surface of the PC steel material, and theresultant PC steel is arranged in concrete in the same manner as thecase of the above-mentioned unbonding PC steel material. Aftertensioning the PC steel material, the steel material is heated by meansof high-frequency heating or the like to allow the thermo-curingcomposition applied on the steel material to be cured, causing adhesionbetween the PC steel material and the concrete. However, in thistechnique, since the tendon which is being tensioned is heated, thestrength of the tendon may be decreased due to the heating, which isvery risky. In addition, it is difficult to accurately heat only certainmaterial region in massive concrete structure, which leads thedisadvantage that complete adhesion along the whole length of the steelwith concrete is impossible.

From the view point of solving these problems, in Japanese ExaminedPatent Publication No. HEI 8-11791 (1996), is proposed a technique thatsecures adhesion between concrete and PC tendon while exerting anti-rustand anti-corrosion effects of the PC tendon without causing theabove-mentioned problems by applying coating material with controlledcuring time (curable coating composition) on surfaces of the PC tendon.

A curable composition used in this technique is based on epoxy resin,blended with potential curing agent such as dihydrazides,diphenyldiaminosulfone, dicyan diamide, imidazole and derivativesthereof, and curing accelerator such as tertiary amine compound ifnecessary.

Development of such a technique enabled effective exertion of functionsof the PC tendon, however, this technique still has a little problem tobe solved. Specifically, in the case of a massive concrete structure,since the exothermic temperature after casting concrete exceeds 90° C.and the high temperature is retained for a long time, such a situationoccurs that the curable coating composition unintendedly starts curing,and the PC tendon cannot be tensioned after hardening of the concrete.

As a technique that can be used under high exothermic temperature duringhardening of concrete, also proposed is a technique that is available athigh temperatures by controlling the curing time by applying curablecoating composition containing epoxy resin and moisture curing agent onsurface of PC tendon (see for example, Japanese Unexamined PatentPublication No. 2000-281967). In this technique, ketimine is used as themoisture curing agent.

The above-mentioned ketimine reacts with moisture to generate curingagent. Industrially produced ketimine is primary amine blocked byketones at a blocking percentage of about 80 to 90%; hence, it includesabout 10 to 20% of remaining active amines. Therefore, in such a curablecoating material, since the remaining active amines gradually increasethe viscosity, storage stability is not satisfactory. That is, incurable coating composition having insufficient storage stability, theviscosity increases due to reactions occurring before it is applied onPC tendon after production thereof, which may impair usability incoating operation and reduce the life of the product.

The present invention has been completed under the above circumstance,and it is an object of the present invention to provide coatingcomposition for PC tendon, enabling effective tensioning even afterhardening of concrete when applied to massive concrete structure, whileexhibiting excellent storage stability.

DISCLOSURE OF THE INVENTION

A coating composition for PC tendon according to the present inventionthat achieved the above object is a composition to be used for applyingon surface of the PC tendon. This composition comprises epoxy resin,multifunctional isocyanate compound, calcium oxide and water. Herein,curing time thereof is adjusted so that tensioning by the PC tendon canbe exerted 30 days or later after casting of concrete.

The epoxy resin used in the coating composition according to the presentinvention preferably has two or more epoxy groups and less than onehydroxyl group on an average in one molecule. Additionally, the water ispreferably contained in a ratio of 0.5 to 2.0 by equivalent relative tothe isocyanate group.

Advantageously, the composition according to the present inventionfurther comprises water-absorbing polymer as necessary. Suchwater-absorbing polymer is preferably contained in a content of about 5to 30% by mass in the composition.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to realize a coating composition for PC tendon that can achievethe above object, the present inventors studied from various points ofview. As a result, the present inventors found that the above object issuccessively achieved when the curing time is adjusted so thattensioning by the tendon comes into effective 30 days or later aftercasting of the concrete by defining chemical composition of the abovecomposition, and accomplished the present invention.

An epoxy resin that is a component constituting the coating compositionaccording to the present invention preferably has, but not limited to,two or more epoxy groups on an average in one molecule. Examples of suchan epoxy resin may include: polyglycidyl compounds of polyphenol such as2,2-bis(4-hydroxyphenyl)propane (commonly called “bisphenol A”),bis(4-hydroxyphenyl)methane (commonly called “bisphenol F”),1,1-bis(4-hydroxyphenyl)ethane (commonly called “bisphenol AD”), 2,2-bis(3,5-dibromo-4-hydroxyphenyl) propane (commonly called “TBA”),hydroquinone and resorcin; polyalcohols such as ethylene glycol andglycerin; and polyglycidyl compounds of multiple carboxylic acids suchas phthalic acid.

Among the above epoxy resins, when an epoxy resin having one or morehydroxyl groups in one molecule is used, it is preferred to useanhydride or the like so that the number of hydroxyl groups is less thanone. If epoxy resin having one or more hydroxyl groups in one moleculeis used, the viscosity becomes significantly large by reaction withcuring agent, resulting in reduction of storage stability.

In the coating composition according to the present invention, thecuring time of the epoxy resin is adjusted by blending multifunctionalisocyanate compound as curing agent and water (water-absorbing polymeras necessary) in an appropriate ratio. Examples of the usable curingagent may include various types of multifunctional isocyanate compoundsdescribed in the following (1) to (10).

(1) Aliphatic Polyisocyanates

Ethylene diisocyanate, trimethylene diisocyanate, tetramethylenediisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate,nonamethylene diisocyanate, 2,2-dimethylpentane diisocyanate,2,2,4-trimethylhexamethylene diisocyanate, decamethylene diisocyanate,buthene diisocyanate, 1,3-butadiene-1,4-diisocyanate,2,4,4-trimethylhexamethylene diisocyanate, 1,6,11-undeca triisocyanate,1,3,6-hexamethylene triisocyanate,1,8-diisocyanate-4-isocyanatemethyloctane,2,5,7-trimethyl-1,8-diisocyanate-5-isocyanatemethyloctane,bis(isocyanateethyl)carbonate, bis(isocyanateethyl)ether,1,4-butyleneglycol dipropylether-ω, ω′-diisocyanate, lysine diisocyanatemethyl ester, lysine triisocyanate,2-isocyanateethyl-2,6-diisocyanateethyl-2,6-diisocyanatehex anoate,2-isocyanatepropyl-2,6-diisocyanatehexanoate, xylene diisocyanate,bis(isocyanateethyl)benzene, bis(isocyanatepropyl) benzene, α, α, α′,α′-tetramethylxylene diisocyanate, bis(isocyanatebutyl)benzene,bis(isocyanatemethyl)naphthalene, bis(isocyanatemethyl)diphenyl ether,bis(isocyanateethyl)phthalate, mesitylene triisocyanate,2,6-di(isocyanatemethyl)furan, and the like.

(2) Alicyclic Polyisocyanates

Isophorone diisocyanate, bis(isocyanatemethyl)cyclohexane,4,4′-dicyclohexylmethane-diisocyanate, cyclohexane diisocyanate,methylcyclohexane diisocyanate, dicyclohexyldimethylmethanediisocyanate, 2,2-dimethyldicyclohexylmethane diisocyanate,bis(4-isocyanate-n-butylidene)pentaerythritol, dimer acid diisocyanate,2-isocyanatemethyl-3-(3-isocyanatepropyl)-5-isocyanatemethy1-bicyclo[2,2,1]heptane,2-isocyanatemethyl-3-(3-isocyanatepropyl)-6-isocyanatemethy1-bicyclo[2,2,1]heptane,2-isocyanatemethyl-2-(3-isocyanatepropyl)-5-isocyanatemethy1-bicyclo[2,1,1]heptane,2-isocyanatemethyl-2-(3-isocyanatepropyl)-6-isocyanatemethy1-bicyclo[2,1,1]heptane,2-isocyanatemethyl-3-(3-isocyanatepropyl)-6-(2-isocyanateethyl-bicyclo[2,2,1]heptane,2-isocyanatemethyl-3-(3-isocyanatepropyl)-6-(2-isocyanateethyl)-bicyclo[2,1,1]heptane,2-isocyanatemethyl-2-(3-isocyanatepropyl)-5-(2-isocyanateethyl)-bicyclo[2,1,1]heptane,2-isocyanatemethyl-2-(3-isocyanatepropyl)-6-(2-isocyanateethyl)-bicyclo[2,1,1]heptane,2-isocyanatemethyl-2-(3-isocyanatepropyl)-6-(2-isocyanateethyl)-bicyclo[2,2,1]heptane,2-isocyanatemethyl-3-(3-isocyanatepropyl)-6-(2-isocyanateethyl)-bicyclo[2,2,1]heptane, 2,5-bisisocyanatemethyl norbornane,2,6-bisisocyanatemethyl norbornane, and the like.

(3) Aromatic Polyisocyanates

Phenylene diisocyanate, tolylene diisocyanate, ethylphenylenediisocyanate, isopropylenephenylene diisocyanate, dimethylphenylenediisocyanate, diethylphenylene diisocyanate, diisopropylphenylenediisocyanate, trimethylbenzene triisocyanate, benzene triisocyanate,naphthalene diisocyanate, methylnaphthalene diisocyanate, biphenyldiisocyanate, 4,4′-diphenylmethane diisocyanate,3,3′-dimethyldiphenylmethane-4,4′-diisocyanate,dibenzyl-4,4′-diisocyanate, bis(isocyanatephenyl)ethylene,3,3′-dimethoxybiphenyl-4,4′-diisocyanate, triphenylmethanetriisocyanate, polymeric MDI “COSMONATE M-200” (trade name) availablefrom Mitsui Takeda Chemicals, Inc., naphthalene triisocyanate,diphenylmethane-2,4,4′-triisocyanate,3-methyldiphenylmethane-4,6,4′-triisocyanate,4-methyl-diphenylmethane-3,5,2′,4′,6′-pentaisocyanate,phenylisocyanatemethyl isocyanate, phenylisocyanateethylethylisocyanate, tetrahydronaphthylene diisocyanate, hexahydrobenzenediisocyanate, hexahydrodiphenylmethane-4,4′-diisocyanate, diphenyletherdiisocyanate, ethyleneglycol diphenylether dilsocyanate,1,3-propyleneglycol diphenylether diisocyanate, benzophenonediisocyanate, diethyleneglycol diphenylether diisocyanate, dibenzofurandiisocyanate, carbazole diisocyanate, ethylcarbazole diisocyanate,dichlorocarbazole diisocyanate, and the like.

(4) Sulfur-Containing Aliphatic Isocyanates

Thiodiethyl diisocyanate, thiopropyl diisocyanate, thiodihexyldiisocyanate, dimethylsulfone diisocyanate, dithiodimethyl diisocyanate,dithiodiethyl diisocyanate, dithiopropyl diisocyanate,dicyclohexylsulfide-4,4′-diisocyanate, and the like.

(5) Aromatic Sulfide Type Isocyanates

Diphenylsulfide-2,4′-diisocyanate, diphenylsulfide-4,4′-diisocyanate,3,3′,4,4′-diisocyanatebenzylthioether, bis(4-isocyanatemethylbenzene)sulfide, 4,4′-methoxybenzenethioglycol-3,3′-diisocyanate, and the like.

(6) Aliphatic Disulfide Type Isocyanates

Diphenyldisulfide-4,4′-diisocyanate,2,2′-dimethyldiphenyldisulfide-5,5′-diisocyanate,3,3′-dimethyldiphenyldisulfide-5,5′-diisocyanate,3,3′-dimethyldiphenyldisulfide-6,6′-diisocyanate,4,4′-dimethyldiphenyldisulfide-5,5-diisocyanate,3,3′-dimethoxyphenyldisulfide-4,4′-diisocyanate,4,4′-dimethoxydiphenyldisulifide-3,3′-diisocyanate, and the like.

(7) Aromatic Sulfone Type Isocyanates

Diphenylsulfone-4,4-diisocyanate, diphenylsulfone-3,3′-diisocyanate,benzidinesulfone-4,4′-diisocyanate,diphenylmethanesulfone-4,4′-diisocyanate,4-methyldiphenylmethanesulfone-2,4′-diisocyanate,4,4′-dimethoxydiphenylsulfone-3,3′-diisocyanate,3,3′-dimethoxy-4,4′-diisocyanate dibenzylsulfone,4,4′-dimethyldiphenylsulfone-3,3′-diisocyanate,4,4′-di-tert-butyldiphenylsulfone-3,3′-diisocyanate,4,4′-methoxybenzeneethylenedisulfone-3,3′-diisocyanate,4,4′-dichlorodiphenylsulfone-3,3′-diisocyanate, and the like.

(8) Sulfonic Acid Ester Type Isocyanates

4-methyl-3-isocyanatebenzenesulfonyl-4′-isocyanatephenol ester,4-methoxy-3-isocyanatebenzenesulfonyl-4′-isocyanatephenol ester, and thelike.

(9) Aromatic Sulfonic Acid Amide Type Isocyanates

4,4-dimethylbenzenesulfonyl-ethylenediamine-4,4′-diisocyanate,4,4-dimethoxybenzenesulfonyl-ethylenediamine-3,3′-diisocyanate,4-methyl-3-isocyanatebenzenesulfonylanilide-4-methyl-3′-iso cyanate, andthe like.

(10) Sulfur-Containing Heterocyclic Compounds

Thiophene-2,5-diisocyanate, thiophene-2,5-diisocyanatemethyl,1,4-dithiane-2,5-diisocyanate, 1,4-dithiane-2,5-diisocyanatemethyl, andthe like.

Alkyl-substituted compounds, alkoxy-substituted compounds,nitro-substituted compounds, blend polymer type modified compounds withpolyalcohol, carbodiimide-modified compounds, urea-modified compounds,buret-modified compounds, and products of dimerization or trimerizationreactions of the above compounds can be used. Multifunctional isocyanatecompounds other than the above compounds may be used. As themultifunctional isocyanate compound of the present invention, a kind ofthese multifunctional isocyanate compounds or the mixture of more thanone kind of these compounds can be used.

Among these compounds, from the view point of availability ofmultifunctional isocyanate compounds, tolylene diisocyanate,4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate,isophorone diisocyanate, 2,5-bisisocyanatemethyl norbornane, α, α, α′,α′-tetramethylxylylene diisocyanate,2,6-bisdiisocyanatemethylnorbornane,4,4′-dicyclohexylmethanediisocyanate, trimethylhexamethylenediisocyanate and derivatives thereof can be preferably used.

From the view point of curing of the resultant coating composition,hexamethylene diisocyanate, isophorone diisocyanate,2,5-bisisocyanatemethyl norbornane, α, α, α′, α′-tetramethylxylylenediisocyanate, 2,6-bisisocyanatemethylnorbornane,4,4′-dicyclohexylmethanediisocyanate, trimethylhexamethylenediisocyanate and derivatives thereof can be especially preferably used.

From the view point of storage stability of the coating composition,4,4′-dicyclohexylmethanediisocyanate, isophorone diisocyanate, α, α, α′,α′-tetramethylxylylene diisocyanate can be preferably used.

Curing property (curing time) of epoxy resin can be adjusted dependingon the blending amount of the above multifunctional isocyanate compound.In the present invention, it is preferred to blend so that the ratio ofepoxy group/isocyanate group (ratio by equivalent) falls within therange of 1.000/0.017 to 1.000/0.17. When the epoxy group/isocyanategroup (ratio by equivalent) is smaller than 1.000/0.017, curing is tooslow. On the other hand, when it is larger than 1.000/0.17, curing istoo fast. The above range is more preferably about 1.000/0.034 to1/0.154.

The coating composition according to the present invention comprisescalcium oxide. Calcium oxide is useful for preventing occurrence offoaming by trapping carbon dioxide gas generated in the system. In orderto bring such an action into effective, the blending amount of calciumoxide is preferably at least approximately equal to the amount (ratio byequivalent) of isocyanate group.

Water in the coating composition of the present invention reacts withthe multifunctional isocyanate compound to generate primary amine whichreacts with the epoxy resin to form cross-linked structure, wherebytoughness is afforded. In order to bring such an action effective, theadding amount of water (in total considering water originated from rawmaterial and generated during production processes) is preferablyadjusted to fall within the range of 0.5 to 2.0 (ratio by equivalent)relative to the isocyanate group. When the above equivalent ratio(water/isocyanate group) is smaller than 0.5, generation of primaryamine is reduced. On the other hand, when it is larger than 2.0, theremaining water will deteriorate physical properties.

The coating composition according to the present inventionadvantageously comprises water-absorbing polymer as necessary, and thiswater-absorbing polymer is useful for keeping the water content in thecomposition constant. In order to bring such an action effective, thecontent of water-absorbing polymer is preferably about 5 to 30% by massin the composition. A content of the water-absorbing polymer of lessthan 5% by mass will reduce the water retention in the system, while acontent exceeding 30% by mass will deteriorate physical properties inthe system. Examples of the water-absorbing polymer which can be used inthe present invention may include acrylic acid polymers partiallycross-linked with sodium salt, “AQUALIC CA ML-20”, “AQUALIC K4”,“AQUALIC H2”, “AQUALIC H3” and the like (trade names, available fromNippon Shokubai Co., Ltd.).

The coating composition according to the present invention may be usedtogether with calcium carbonate, talc, silica, coloring pigment or thelike that are commonly used as fillers for paint or adhesive asnecessary. These fillers are useful for adjusting viscosity andthixotropic property. Organic solvents not having an active hydrogen,dispersing agents, antifoaming agents, or the like can also be used foradjusting the viscosity.

As a method for producing the coating composition according to thepresent invention, for example, the following method can be givenwithout any limitation. First, epoxy resin having two or more epoxygroups and having less than one hydroxyl group on an average in onemolecule, and multifunctional isocyanate compound as curing agent areblended in a ratio of 1.000/0.017 to 1.000/0.170 (ratio by equivalent).Then, calcium oxide, water, and as necessary, water-absorbing polymerand filler as described above are added and mixed by stirring. Aftercompletion of mixing, deforming is conducted in vacuum to obtain acoating material.

When used in a post-tensioning system, the coating composition accordingto the present invention is applied on the surface of PC tendon, and theresultant tendon is covered with sheath member consisting of resin suchas polyethylene with irregularities formed on its surface and innerface. It takes about two weeks after casting of concrete to acquire apredetermined strength, and may take about another two weeks untiltensioning depending on the construction schedule. Therefore, the curingtime of the coating composition should be adjusted so that tensioning isallowed for at least 30 days after casting of the concrete. Furthermore,it is preferably adjusted to cure in one to two years after tensioningof the PC tendon.

In order to exert the effect of the coating composition according to thepresent invention effectively, the coating thickness of the coatingcomposition is preferably 20 μm or more. This is because when thecoating thickness is less than 20 μm, the breaking off at the boundaryof the PC steel material and the concrete or the sheath member is notsufficient at the time of tensioning, so that the friction coefficientis large. As a coating method, any method can be applied withoutlimitation as far as uniform coating on the surface of the PC tendon canbe realized. An example thereof may include a coating method capable ofuniformly coating with an intended amount of resin, wherein a steelmaterial is allowed to pass through a resin box filled with resin, andexcess resin is removed through a hole which is provided at an outlet ofthe resin box and has the same diameter as that of the steel materialafter coating.

EXAMPLES

In the following, the present invention will be described in more detailby way of examples. The following examples are not intended to limit thepresent invention, and any modification of design from the above orbelow description is encompassed in a technical scope of the presentinvention.

Production Example 1

Epoxy resin R140 available from Mitsui Chemicals, Inc. (72.30 g),calcium oxide (13.77 g), calcium carbonate (10.21 g) and AEROSIL (1.38g) were introduced into a mixer, and mixed for 30 minutes understirring. The water content was then measured. The water content was0.02%.

Next, isophorone diisocyanate (IPDI) (2.17 g) was added and mixed for 10minutes under stirring. Water (0.17 g) wad then added and mixed for 10minutes under stirring. Then, defoaming treatment was conducted underreduced pressures to obtain a coating composition.

The obtained coating composition was applied on a PC steel material(steel rod) having a diameter of 12.7 mm in a thickness of 0.5 to 1.0mm. Then it was covered with a sheath member consisting of polyethylenewith irregularities formed on its surface and inner face, and buried inconcrete. After 30 days, the coating composition was removed from theconcrete, and the viscosity of the coating composition was measured(provided that the measurement concerning the coating composition ofProduction Example 1 to 12 was conducted only when the coatingcomposition was soft enough to allow measurement of viscosity), andafter 1.5 years, the coating composition was removed again from theconcrete, and the degree of hardness of the coating composition wasmeasured with a type-D durometer. In addition, the coating compositionwas put into a glass airtight container and stored in atemperature-controlled room at 23° C., and storage stability wasevaluated from change in viscosity with time.

The maximum exothermic temperature during concrete placing was 95° C.Viscosity after 30 days and viscosity in evaluation of storage stabilitywere measured by a Brookfield viscometer and an E-type viscometer,respectively.

Production Example 2

Epoxy resin R140, available from Mitsui Chemicals, Inc. (72.17 g),calcium oxide (13.74 g), calcium carbonate (10.20 g) and AEROSIL (1.37g) were put into a mixer, and mixed for 30 minutes under stirring. Thewater content was then measured. The water content was 0.02%.

Next, IPDI (2.17 g) was added and mixed for 10 minutes under stirring.Water (0.35 g) was then added and mixed for 10 minutes under stirring.Then, defoaming treatment was conducted under reduced pressures toobtain a coating composition. The obtained coating composition wasevaluated for viscosity, degree of hardness and storage stability insimilar manner as described in Production Example 1.

Production Example 3

Epoxy resin R140 available from Mitsui Chemicals, Inc. (72.05 g),calcium oxide (13.71 g), calcium carbonate (10.17 g) and AEROSIL (1.37g) were put into a mixer, and mixed for 30 minutes under stirring. Watercontent was then measured. The water content was 0.02%.

Next, IPDI (2.17 g) was added and mixed for 10 minutes under stirring.Water (0.53 g) was then added and mixed for 10 minutes under stirring.Then, defoaming treatment was conducted under reduced pressures toobtain a coating composition. The obtained coating composition wasevaluated for viscosity, degree of hardness and storage stability insimilar manner as described in Production Example 1.

Production Example 4

Epoxy resin R140 available from Mitsui Chemicals, Inc. (70.41 g),calcium oxide (13.41 g), calcium carbonate (9.94 g) and AEROSIL (1.34 g)were put into a mixer, and mixed for 30 minutes under stirring. Watercontent was then measured. The water content was 0.02%.

Next, IPDI (4.22 g) was added and mixed for 10 minutes under stirring.Water (0.68 g) was then added and mixed for 10 minutes under stirring.Then, defoaming treatment was conducted under reduced pressures toobtain a coating composition. The obtained coating composition wasevaluated for viscosity, degree of hardness and storage stability insimilar manner as described in Production Example 1.

Production Example 5

Epoxy resin R140 available from Mitsui Chemicals, Inc. (68.72 g),calcium oxide (13.08 g), talc (9.69 g) and AEROSIL (1.31 g) were putinto a mixer, and mixed for 30 minutes under stirring. The water contentwas then measured. The water content was 0.02%.

Next, IPDI (6.19 g) was added and mixed for 10 minutes under stirring.Water (1.01 g) was then added and mixed for 10 minutes under stirring.Then, defoaming treatment was conducted under reduced pressures toobtain a coating composition. The obtained coating composition wasevaluated for viscosity, degree of hardness and storage stability insimilar manner as described in Production Example 1.

Production Example 6

Epoxy resin R140 available from Mitsui Chemicals, Inc. (68.87 g),calcium oxide (13.11 g), calcium carbonate (9.72 g) and AEROSIL (1.31 g)were put into a mixer, and mixed for 30 minutes under stirring. Thewater content was then measured. The water content was 0.02%.

Next, a water-absorbing polymer (AQUALIC CA ML-20) (4.76 g) and water(0.16 g) were added, and mixed for 10 minutes under stirring. IPDI (2.07g) was then added, and mixed for 10 minutes under stirring. Then,defoaming treatment was conducted under reduced pressures to obtain acoating composition. The obtained coating composition was evaluated forviscosity, degree of hardness and storage stability in similar manner asdescribed in Production Example 1.

Production Example 7

Epoxy resin R140 available from Mitsui Chemicals, Inc. (69.76 g),calcium oxide (13.09 g), calcium carbonate (9.71 g) and AEROSIL (1.31 g)were put into a mixer, and mixed for 30 minutes under stirring. Thewater content was then measured. The water content was 0.02%.

Next, water-absorbing polymer (AQUALIC CA ML-20) (4.75 g) and water(0.32 g) were added, and mixed for 10 minutes under stirring. IPDI (2.06g) was then added and mixed for 10 minutes under stirring. Then,defoaming treatment was conducted under reduced pressures to obtain acoating composition. The obtained coating composition was evaluated forviscosity, degree of hardness and storage stability in similar manner asdescribed in Production Example 1.

Production Example 8

Epoxy resin R140 available from Mitsui Chemicals, Inc. (63.83 g),calcium oxide (12.16 g), calcium carbonate (9.01 g) and AEROSIL (1.22 g)were put into a mixer, and mixed for 30 minutes under stirring. Thewater content was then measured. The water content was 0.02%.

Next, water-absorbing polymer (AQUALIC CA ML-20) (9.09 g) and water(0.92 g) were added, and mixed for 10 minutes under stirring. IPDI (3.77g) was then added and mixed for 10 minutes under stirring. Then,defoaming treatment was conducted under reduced pressures to obtain acoating composition. The obtained coating composition was evaluated forviscosity, degree of hardness and storage stability in similar manner asdescribed in Production Example 1.

Production Example 9

Epoxy resin R140 available from Mitsui Chemicals, Inc. (56.77 g),calcium oxide (10.81 g), calcium carbonate (8.02 g) and AEROSIL (1.08 g)were put into a mixer, and mixed for 30 minutes under stirring. Thewater content was then measured. The water content was 0.02%.

Next, water-absorbing polymer (AQUALIC CA ML-20) (16.67 g) and water(1.63 g) were added, and mixed for 10 minutes under stirring. IPDI (5.02g) was then added and mixed for 10 minutes under stirring, further water(1.63 g) was added, and mixed for 10 minutes under stirring. Then,defoaming treatment was conducted under reduced pressures to obtain acoating composition. The obtained coating composition was evaluated forviscosity, degree of hardness and storage stability in similar manner asdescribed in Production Example 1.

Production Example 10

Epoxy resin R140 available from Mitsui Chemicals, Inc. (72.42 g), IPDI(2.17 g), calcium oxide (13.80 g), calcium carbonate (10.23 g) andAEROSIL (1.38 g) were put into a mixer, and mixed for 30 minutes understirring. The mixture was subjected to defoaming treatment under reducedpressures to obtain a coating composition.

The obtained coating composition was evaluated for viscosity, degree ofhardness and storage stability in similar manner as described inProduction Example 1.

Production Example 11

Epoxy resin R140 available from Mitsui Chemicals, Inc. (56.92 g), benzylalcohol (6.32 g), dicyan diamide (DICY) (4.43 g), 2,4,6-tris(dimethylaminomethyl)phenol (TAP) (0.08 g), talc (31.62 g) and AEROSIL(0.63 g) were put into a mixer, and mixed for 30 minutes under stirring.The mixture was subjected to defoaming treatment under reduced pressuresto obtain a coating composition. The obtained coating composition wasevaluated for viscosity, degree of hardness and storage stability insimilar manner as described in Production Example 1.

Production Example 12

Epoxy resin R140 available from Mitsui Chemicals, Inc. (59.88 g),ketimine [“Epicure H-3” (trade name) available from Japan Epoxy ResinsCo., Ltd.] (5.99 g), calcium carbonate (29.94 g) and benzyl alcohol(4.19 g) were put into a mixer, and mixed for 30 minutes under stirring.The mixture was subjected to defoaming treatment under reduced pressuresto obtain a coating composition. The water content at this time was0.02%. The obtained coating composition was evaluated for viscosity,degree of hardness and storage stability in similar manner as describedin Production Example 1.

Respective blending ratios of the coating compositions described aboveare shown in Tables 1 and 2 below. Viscosity, degree of hardness andstorage stability of each coating composition are shown in Table 3below. TABLE 1 Production Example Blending amount 1 2 3 4 5 Epoxy resin(R140) (g) 72.30 72.17 72.05 70.41 68.72 IPDI (g) 2.17 2.17 2.17 4.226.19 Calcium oxide (g) 13.77 13.74 13.71 13.41 13.08 Calcium carbonate(g) 10.21 10.20 10.17 9.94 — Talc (g) — — — — 9.69 AEROSIL (g) 1.38 1.371.37 1.34 1.31 DICY (g) — — — — — TAP (g) — — — — — Ketimine (g) — — — —— Benzyl alcohol (g) — — — — — Water (g) 0.17 0.35 0.53 0.68 1.01 Ratioby equivalent 1.000/ 1.000/ 1.000/ 1.000/ 1.000/ (isocyanate/water)0.500 1.000 1.500 1.000 1.000

TABLE 2 Production Example Blending amount 6 7 8 9 10 11 12 Epoxy resin(R140) (g) 68.87 68.76 68.83 56.77 72.42 56.92 59.88 IPDI (g) 2.07 2.063.77 5.02 2.17 — — Calcium oxide (g) 13.11 13.09 12.16 10.81 13.80 — —Calcium carbonate (g) 9.72 9.71 9.01 8.02 10.23 — — Talc (g) — — — — —31.62 29.94 AEROSIL (g) 1.31 1.31 1.22 1.08 1.38 0.63 — Water-absorbingpolymer (g) 4.76 4.75 9.09 16.67 — — — DICY (g) — — — — — 4.43 — TAP (g)— — — — — 0.08 — Ketimine (g) — — — — — — 5.99 Benzyl alcohol (g) — — —— — 6.32 4.19 Water (g) 0.16 0.32 0.92 1.63 0 0 0 Ratio by equivalent1.000/ 1.000/ 1.000/ 1.000/ 1.000/ — — (isocyanate/water) 0.500 1.0001.500 2.000 1.0

TABLE 3 Storage stability Viscosity directly Hardness after afterViscosity after 1.5 years production Viscosity after Production 30 days(Type-D (Pa · s/ one month Example (Pa · s/23° C.) durometer) 23° C.)(Pa · s/23° C.) 1 610 46 65 1.03 2 650 43 65 1.03 3 640 45 60 1.02 4 68042 66 1.03 5 590 45 65 1.03 6 680 46 70 1.02 7 670 45 69 1.03 8 710 4775 1.03 9 730 48 78 1.01 10 530 0 63 1.02 11 incapable 52 70 1.03measurement 12 2600 48 62 2.15

From these results, we can discuss as follows. First, the coatingcompositions produced in Production Examples 1 to 9 satisfy all therequirements defined in the present invention. Therefore, it is foundthat tensioning was possible 30 days or later after casting of theconcrete, the composition could be cured after 1.5 years and hadexcellent storage stability with low thickening factor after one month.

To the contrary, the coating compositions produced in ProductionExamples 10 to 12 do not satisfy either of the requirements defined inthe present invention, so that they were inferior in eithercharacteristic.

The coating material produced in Production Example 10 was superior instorage stability, and tensioning was possible after 30 days. However,since generation of primary amine was insufficient, curing wasinsufficient after 1.5 years. The coating material produced inProduction Example 11 was superior in storage stability. However, sincethe curing starts, tensioning after 30 days or later could not berealized. The coating material produced in Production Example 12 wasinferior in storage stability with high magnification of viscosity after30 days because the remaining active amine caused curing even thoughtensioning after 30 days or later was possible.

INDUSTRIAL APPLICABILITY

The present invention constituted as described above makes it possibleto realize coating composition for PC tendon, by which tensioning 30days or later after casting of concrete is possible. The coatingcomposition can be cured at a predetermined time after tensioning andhas excellent storage stability. By using the coating compositionaccording to the present invention and bringing out its suchcharacteristics described above, tensioning is possible when exothermictemperature after casting of concrete exceeds 90° C. in the case of amassive concrete structure, and the tendon with anti-rust andanti-corrosion effect can be provided and sufficient adhesion betweenthe concrete and the PC tendon can be realized. Furthermore, since thecoating composition has excellent storage stability, it is usefulbecause deterioration of operability due to thickening during use can beavoided.

1. A coating composition for a tendon for prestressed concrete; whereinbeing applied on surface of the tendon; comprising epoxy resin,multifunctional isocyanate compound, calcium oxide and water; and curingtime thereof is adjusted so that tensioning by the tendon can be exerted30 days or later after casting of the concrete.
 2. The coatingcomposition for a tendon for prestressed concrete according to claim 1,wherein said epoxy resin has two or more epoxy groups and less than onehydroxyl group by an average in one molecule.
 3. The coating compositionfor a tendon for prestressed concrete according to claim 1, wherein saidwater is contained in a ratio of 0.5 to 2.0 by equivalent relative tothe isocyanate group.
 4. The coating composition for a tendon forprestressed concrete according to claim 2, wherein said water iscontained in a ratio of 0.5 to 2.0 by equivalent relative to theisocyanate group.
 5. The coating composition for a tendon forprestressed concrete according to claim 1, further comprisingwater-absorbing polymer.
 6. The coating composition for a tendon forprestressed concrete according to claim 5, wherein said water-absorbingpolymer is contained in a ratio of 5 to 30% by mass with respect to thecomposition.
 7. The coating composition for a tendon for prestressedconcrete according to claim 2, further comprising water-absorbingpolymer.
 8. The coating composition for a tendon for prestressedconcrete according to claim 3, further comprising water-absorbingpolymer.
 9. The coating composition for a tendon for prestressedconcrete according to claim 4, further comprising water-absorbingpolymer.
 10. The coating composition for a tendon for prestressedconcrete according to claim 7, wherein said water-absorbing polymer iscontained in a ratio of 5 to 30% by mass with respect to thecomposition.
 11. The coating composition for a tendon for prestressedconcrete according to claim 8, wherein said water-absorbing polymer iscontained in a ratio of 5 to 30% by mass with respect to thecomposition.
 12. The coating composition for a tendon for prestressedconcrete according to claim 9, wherein said water-absorbing polymer iscontained in a ratio of 5 to 30% by mass with respect to thecomposition.